Scientific researchers often require the identification of the constituent parts of chemical and biological samples. For example, particular experiments may require determination of the homogeneity, identification of proteins, or even the mapping of nucleic acid structures such as DNA and RNA.
The instruments used to perform such analyses typically operate on the principle that molecular species can be isolated from one another by capitalizing on the fact that each species has a unique combination of mass, size, shape, charge, mobility, density, sub-unit structure, or optical emission, absorption, or reflectance. Liquid chromatography (LC), super critical fluid chromatography (SFC), gas chromatography (GC) and capillary zone electrophoresis (CZE) are among the most commonly used separation techniques that take advantage of one or more of these differences in molecular properties.
Capillary zone electrophoresis, for example, makes use of the fact that different ionic species have different mobilities when subjected to an electric field. In a CZE instrument, an extremely thin capillary tube is typically filled with a conductive buffer solution. A small amount of the sample to be analyzed is then introduced into the buffer solution at an inlet end of the capillary tube, and an electrical potential difference is applied across the ends of the tube. The resulting electric field causes the various ions in the sample to begin migrating down the tube. Because of differences in the electrophoretic mobilities of different ions, the various constituents of the sample exit the outlet end of the tube at different times, and in groups of like ions, or so-called `zones`. The chemical or biological makeup of a sample can thus be detected by determining the timing and the concentration of the zones exiting from the tube.
In CZE and similar instruments which rely on separation techniques, it is often advantageous or necessary to connect capillary tubes together. Likewise, it is often necessary to connect capillary tubes to various structures such as detectors, fluid valves, and buffer solution reservoirs, to further process and separate the samples.
A problem generally exists with such apparatus, since the user cannot readily change a particular configuration. For example, researchers often may wish to compare the results when the size of capillary tube is changed, with coated and uncoated tubes, with detectors of different types, and with different flow cells. Furthermore, the optimum configuration of these components typically also depends upon the nature and desired accuracy of the particular information being sought.
It is thus desirable to provide a separation instrument which would permit the user to efficiently connect and disconnect the many operational components such as conductivity, electrochemical, ultraviolet/visible (UV/VIS), and fluorescence detectors of various types, as well as buffer solution reservoirs, and valves.
However, probably because of the extremely small tolerances involved, this has heretofore been thought to be difficult to achieve. For example, the capillary tubes used in CZE instrumentation typically have an outer diameter on the order of 150 to 360 microns, and nominal inner diameters of 50 to 75 microns or less with tolerances as small as a few microns being required in some applications. And yet, the capillary tubes must be accurately aligned with a detector, for example, to avoid creating adverse effects.
U.S. Pat. No. 4,787,656 issued to Ryder and assigned to Hewlett Packard Company discusses a coupling device for connecting capillary tubing. While the coupling device can be used to connect two pieces of tubing together, it is not readily apparent how such a device could be adapted, or that it is even desirable, to permit detachment as well as attachment of capillaries, or how one would provide a quick and easy mechanism for interconnecting various components of an analytic instrument.